This service supports the Microsoft .NET Framework Native Image Generator (NGEN) feature of the .NET Framework Common-Language Runtime. It is used to create platform-specific, optimized versions of .NET Framework applications that have faster performance than applications that have to be compiled by the just-in-time compiler before they can be run.

The service runs either in low priority for important compilations or in idle priority for non-important compilations. After all optimizations that are in the queue are completed, the service shuts down.

This service is installed by default, and the service startup type is Manual. You might have several versions of this service installed by different .NET applications. This service has been renamed Native Image Service in .NET Framework 4.